1. Field of the Invention
The present invention relates to commercial and military applications of microwave circuits related to solid state radar and communication applications.
2. Description of the Related Art
Solid state communication and radars utilize active components and passive radiators to transmit and receive radio frequency signals. Radars use active components and passive radiators to transmit and receive object returns. The special class of radars utilizing phased array antennas is of special interest because of their multi-functionality. These radars provide electronic special scanning capability which far out performs fixed or mechanically steered antennas.
Originally these phased array antennas utilized travelling wave tube technology with a single traveling wave tube that amplified the microwave radar signal before sending it to a power divider which fed several thousand ferrite phase shifters. These ferrite phase shifters provided the electronic steering capability to the antenna (FIG. 1). Another signal path partially common to the transmit path received the return signal and routed it to a low noise amplifier. The losses on the transmit path and the receive path significantly reduced radar energy on target and return detection. These losses were overcome by larger, more expensive, traveling wave tubes which significantly decreased the radar efficiency. A solid state architecture followed that removed a large portion of these losses from phased array radar front ends.
With the invention and development of key technologies (e.g. gallium arsenide, monolithic microwave integrated circuits, and advanced manufacturing technology) a new architecture emerged that revolutionized phased array radar antennas. This architecture utilized transmit/receive modules that contained transmit power-amplifiers which replaced the traveling wave tube and the low noise amplifier (FIG. 2). The power amplifier and the low noise amplifier, considered the active components, were placed within several inches of the radar antenna face. This approach was very attractive because it eliminated a significant portion of the RF/microwave losses that were inefficient and increased cost.
The transmit/receive module contains a solid state microwave monolithic amplifier which transmits and receives through a circulator, connectors, and a passive radiating element. This architecture is a great improvement over the traveling wave tube architecture, but with remaining losses, approximately one half of the power is still lost on transmit and the noise is approximately doubled on receive. The need for improvement is obvious, but the transmit and receive architecture drove the requirement for all of these components between the free space and the active components. Another inefficiency was created by the requirement to transform the device impedances to fifty ohms and then up to several hundred ohms at the radiator. A low loss transmit/receive impedance transformer which reactively matches the device impedances to free space is needed.
The logical approach for the next major stage of radar performance improvement is the active radiator. The active radiator was originally conceived by the government and incorporates active devices in the radiator hardware and eliminates the most significant lossy components. This approach:
(1) eliminates front end RF and microwave signal losses; PA1 (2) reduces hardware complexity; (3) reduces cost; and PA1 (4) increases radar performance.
The related art is represented by the following patents of interest.
U.S. Pat. No. 4,800,393, issued on Jan. 24, 1989 to Brian J. Edward et al., describes a microstrip fed printed dipole with an integral balun and a 180 degree phase shift bit. Edward et al. do not suggest a single balanced to dual unbalanced transformer according to the claimed invention.
U.S. Pat. No. 5,189,434, issued on Feb. 23, 1993 to Ross L. Bell, describes a multi-mode antenna system having plural radiators coupled via hybrid circuit modules. Bell does not suggest a single balanced to dual unbalanced transformer according to the claimed invention.
U.S. Pat. No. 5,313,218, issued on May 17, 1994 to Erik B. Busking, describes an antenna assembly. Busking does not suggest a single balanced to dual unbalanced transformer according to the claimed invention.
U.S. Pat. No. 5,357,223, issued on Oct. 18, 1994 to Olivier Forgeot, describes a connection device between an antenna and a microelectronic enclosure. Forgeot does not suggest a single balanced to dual unbalanced transformer according to the claimed invention.
U.S. Pat. No. 5,565,881, issued on Oct. 15, 1996 to James P. Phillips et al., describes a balun apparatus including impedance transformer having transformation length. Phillips et al. '881 does not suggest a single balanced to dual unbalanced transformer according to the claimed invention.
U.S. Pat. No. 5,594,393, issued on Jan. 14, 1997 to Werner Bischof, describes a microwave line structure. Bischof does not suggest a single balanced to dual unbalanced transformer according to the claimed invention.
U.S. Pat. No. 5,628,057, issued on May 6, 1997 to James P. Phillips et al., describes a multi-port radio frequency signal transformation network. Phillips et al. '057 does not suggest a single balanced to dual unbalanced transformer according to the claimed invention.
U.S. Pat. No. 5,697,088, issued on Dec. 9, 1997 to Wang-Chang Albert Gu, describes a balun transformer. Gu does not suggest a single balanced to dual unbalanced transformer according to the claimed invention.
U.S. Pat. No. 5,705,960, issued on Jan. 6, 1998 to Toru Izumiyama, describes a balanced-to-unbalanced converting circuit. Izumiyama does not suggest a single balanced to dual unbalanced transformer according to the claimed invention.
Japan Patent document 60-64531, published on Apr. 13, 1985, describes an antenna matching unit. Japan '531 does not suggest a single balanced to dual unbalanced transformer according to the claimed invention.
None of the above inventions and patents, taken either singularly or in combination, is seen to describe the instant invention as claimed.